Method and apparatus for processing strip metal



Oct. 17, 1950 M, NE 2,526,296

METHOD AND APPARATUS FOR PROCESSING STRIP METAL Filed Aug. 12, 1943 4 Sheets-Sheet 1 HTTURNEY M. D'. STONE 2,526,296

unmon AND APPARATUS FOR PROCESSING STRIP METAL 4 Sheets-Sheet 2 Filed Aug. 12, 1943 \rTZ/VESSES.

METHOD AND APPARATUS FOR PROCESSING STRIP METAL Filed Aug. 12, 1943 M. D. STONE Oct. 17, 1950 4 Sheets-Sheet 3 )Jlllllllllllllll (Hp Egg Ill

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METHOD AND APPARATUS FOR PROCESSING STRIP METAL I Filed Aug. 12, 1943 4 Sheets-Sheet 4 d INVENTOR.

4 TTOPNE Y Patented Oct. 17, 1950 METHOD AND APPARATUS FOR PROCESSING STRIP IHETAE.

Morris D. Stone, Pittsburgh, Pa., assignor to United Engineering & Foundry Company, Pittsburgh. Pa., a corporation of Pennsylvania Application August 12, 1943, Serial No. 498,389

The invention relates to methods of and mills for processing strips of elastic metal, such as steel, aluminum and copper, whose temper or hardness may be increased by cold stretching the metal beyond its yield point. The typ of strip metal here contemplated is that which is relativelywide and thin when compared with what is known as fiat-wire or banding. Although in several of its important aspects the invention may advantageously be used in the tension processing of non-ferrous strip metal of the character and type stated, it is particularly applicable to the tempering of strip steel, with reference to which it is herein primarily described.

In the manufacture ofmost cold rolled strip steel, such as tin plate, automobile body stock, furniture stock, stainless steel panels, etc., a necessary final production step is tempering the metal to specified hardness, drawability, etc. The normal production cycle for tin plate is hot rollin pickling, cold rolling to reduce the metal, cleaning, annealing, and tempering which is done by cold rolling. In temper rolling the operating conditions are such that only relatively small reduction can be made, one reason for this being that the metal is then quite thin and diflicult to reduce, and the other being that, to avoid staining the metal and interfering with subsequent tinning and other coating, temper rolling is done without the benefit of rolling oil or coolants which are used to facilitate the cold rolling that follows hot rolling. Although the percentage reductions in temper rolling are not greater than about ten per cent for maximum hardness, it is practically impossible with present equipment to take such a reduction in a single pass, even although such pass be through a heavy-duty four-high mill with front and back tension applied to the strip. Both the rolling pressures as measured-in pounds per unit of width of. strip, and the rolling energy as indicated by horsepower hours per'ton are materially higher for the normal temper rolling operations than for either hot rolling or cold reducing rolling comparable reductions, or in some instances for far greater reductions. Thus, temering by rolling is a very difilcult and expensive procedure.

A further disadvantage of tempering steel by rolling is that the ductility and the attending drawability of the metal decreases materially as the temper hardness is increased. Because of this reduction in ductilityin the tin can industry it is now common practice to specify a "hard tin '11 Claims. '(crso-es) plate for can bodies to provide the necessary a strength to avoid fiuting in the formation of the bodies and to .eliminate bulging due to internal gas pressures, and to specify a soft tin pla for can tops which are relatively deep drawn in their formation but whose strength is not of such great importance as that of the bodies. Furthermore, in the shaping and particularly the crimpin of can bodies made from tin plate it is usually necessary to take into consideration the direction of orientation of the grains resulting from the temper rolling of the sheet metal.

One object of the invention is to provide a method of and mill for tempering strip metal at a low cost per ton, in a continuous fashion by stretching the strip beyond its yield point solely by tension progressively applied to the strip from end to end in variable amounts depending upon the temper desired; and a further object is by thus tempering strip metal, particularly strip steel, to improve the grain structure and physical characteristics of the resulting product to the end that it may readily be drawn or otherwise formed without impairment, and may be used as well for the tops as the bodies of tin cans and without regard to the direction of temper rolling.

When sheet metal made from relatively low carbon steel is stretched in its annealed state be-= yond its yield point from about one to some critical per cent,'usually about five per cent (depending upon the chemical analysis, and upon the speed of processing the strip when it is stretched in a. continuous fashion), a slipping of the crystals takes place which is evidenced on the surface of the metal as slip lines at an angle to the direction of stretching, such lines being known as stretcher strains. These slip lines disappear when such sheet metal is elongated beyond the aforesaid critical per cent, and they do not occur when the metal has, within a limited period which is not more than about two days for most steels, been preworked by a roller leveling operation, nor when it has been preworked by cold rolling, the efiect of which lasts for man;' weeks.

When sheet steel is stretched beyond its yield point a roughening of its surfaces takes place. Such roughening and the stretcher strains just explained may or may not be objectionable, depending upon the use that is made of the product. If the product .is to be painted as in furniture stock, or is to be hot coated with a relatively heavy coat of metal, the roughening of the metal is desirable in improving the bond and in increasing the coating thickness, and when this is desired the roughening of the metal surfaces may be increased by passing it between rolls having roughened faces. on the other hand, if the prodnot is to be electroplated or hot-dip coated with metal to produce a smooth bright finish, surface streaks and roughness of the sheet metal objectionably show through the coatings. Where a temper hardened strip having either rough or smooth and unstreaked surface is required, it is desirable, from the point of view of economies in manufacturing and for other reasons, to perform the necessary steps in a single operation while the tempering or other cold processing is being done. Such steps may be preworking by cold rolling with smooth or rough surfaced rolls immediately prior to tension tempering, or final rolling with smooth burnishing or with roughsurfaced rolls immediately following tension tempering, or both preworking and final ro1ling..

A further object of the invention is to provide a method of and mill for cold processing strip .metal whereby in a single operation and in a continuous fashion it may. be cold rolled to preclude the formation of stretcher strains or to roughen its surface or surfaces as desired, and then stretched beyond its yield point solely by tension progressively applied, and then burnished or roughened.

When a strip of metal is being stretched when cold beyond. its yield point it is in a physical state which throughout'this specification and in the claims is designated as the plastic state," and when it is being stretched below its yield point it is in a physical state which for the same purpose is designated as the elastic state. When thin sheet metal is in the plastic state by reason of its ends being engaged and pulled by a stretcher leveler, a phenomenon called guttering may occur which is evidenced by the development of permanent longitudinal corrugations in the metal. Such guttering occurs only in the plastic state of the metal, and is in the nature of lateral cold plastic instability of the metal. It varies with the composition of the metal, the nature of its stress strain curve, its width and length and with itsmetallurgical condition incident to its being in an annealed or cold worked state, and, other factors being the same, its currence varies inversely with relation to the thickness of the metal.

It is a still further object of the invention to provide a method of and mill for cold processing strip metal, whether for tempering, stretcher leveling or other purposes, whereby the strip is stretched beyond its yield point solely by tension and in such'a way as to prevent guttering.

Furtherobjects and advantages of the invention will appear from the following description of the method and of mills for practicing it.

The invention will be further explained with reference to the accompanying drawings of which Fig. 1 is a diagrammatic end view of a group of rolls showing a strip of metal passing through them; Fig. 2 a :plan view of the portion of the strip passing through the rolls shown in Fig. 1, the narrowing of the width of the strip being somewhat exaggerated; Fig. 3 a somewhat diagrammatic vertical central sectional view of a mill equipped with rolls positioned and arranged as shown in Fig. 1, the view including tensioning and other accessories on the entering and delivery sides of the mill; Fig. 4 a somewhat diagrammatic side view of the delivery side of the mill shown in Fig. 3; Figs. 5 and 6 diagrammatic face views of mills equipped with rolls the same as shown in Figs. 3 and 4, illustrating modifications of roll drives: and Figs. 7, 8, 9 and 10 diagrammatic end views of mills showing alternative arrangements of rolls.

In the practice of the method provided by this invention a strip of metal which is wide with relation to its thickness is progressively tensioned beyond its yield point by wrapping the strip partially around parallel drag and pull rolls frictionally to engage a relatively large portion of the face of each, a portion of the strip between these rolls being free from engagement with them. As shown in Fig. 1, this may be done by wrapping a strip S partially around a drag roll D and a pull roll P which are so spaced from each other that there is a gap between their adjacent faces in which the strip is free from engagement with the rolls. The pull roll is driven at a peripheral speed greater than that of the drag roll progressively to stretch beyond its yield point the portion of the strip that moves continuously from the drag to the pull roll. As explained hereinafter in greater detail with reference to the drawings, such driving of the drag and pull rolls may be effected by separate motors which are controlled by suitable electric equipment to the end that the motor connected to the drag roll acts during the tensionstretching of the strip as a regenerative brake of predetermined known eifectiveness with relation to the nected to it. In the alternative, as also illustrated in the drawings and hereinafter described in greater detail, the drag and pull rolls may be positively geared to each other to effect a desired difference in the peripheral speeds of the rolls to perform the tension stretching operation, different gear ratios being substituted for other desired tensioning operations, or the drag and pull rolls may be coupled together by a differential gear mechanism that is suitably driven and controlled by diiferent motors.

A portion of the strip that moves continuously from drag roll D to pull roll P is in the plastic state induced by the tensioning of it, and the portions of the strip immediately adjoining that which is in the plastic state are in the elastic state, as both such states are defined above. Referring to Fig. l, the unsupported length of the strip between its point of tangency T with drag roll D and its point of tangency T with the pull roll P is in the plastic state which is induced by its being tensioned materially beyond its yield point, such portion having no frictional force resisting its tensioning. From the line of tangency T elongation of the portion of the strip wrapped upon the drag roll is progressively resisted by frictional engagement of the strip with the roll,

which resistance accumulates until, at a line generally designated as Y the strip is no longer tensioned beyond its yield point. Therefore a portion of the strip wrapped upon drag roll D in a counter-clockwise direction from the yield point line Y is in the elastic state. Similarly, the portion of the strip between its line of tangency T with pull roll P extending to a yield point line generally indicated at Y is in the plastic state and is joined by a portion of the strip in the elastic state beyond yield point line Y in a clockwise direction.

The unsupported length of the plastic state portion of the strip between its lines of tangency T and T with rolls D and P, respectively, is made short enough with relation to the width of the strip to maintain the strip laterally stable and consequently free from longitudinal guttering. Because the Plastic state portions of the any tendency of such portions to gutter. I-

have found that in tension tempering strip steel containing about 0.10 per cent carbon and having a thickness of about .01 of an inch the unsupported length of the strip between its points of I tangency T and T should not be greater than two-thirds of the width of the strip to prevent guttering for all elongations of the strip that may be afiected up to its necking point, which is about atwenty per cent elongation. For the commercial range of thickness of low carbon tin plate strip the unsupported plastic state length should not be greater than the width of the strip, the length permissably increasing as the thickness increases. For. the strips of any material the maximum length of the unsupported strip with relation to its width to maintain the strip laterally stable and consequently free from longitudinal guttering may be determined by progressively increasing such unsupported length until guttering occurs.

In a manner presently to be explained, a strip being cold processed is preferably tensioned on both the entering and delivery sides of the mill. To prework the strip while it is being subsequently progressively tensioned beyond its yield point in the manner explained, a working ro l is preferably positioned above drag roll D to cooperate with it in cold rolling the strip. Such cold rolling takes place at and immediatey adjacent to the meeting lines of rolls l and D, and while the strip is thus being cold rolled the metal thereof is in a more fluid state than it is before it enters and after it leaves the bite of the rolls. Just beyond the bite of the rolls the metal of the strip is in the elastic state in which'it remains until it reaches the yield point line Y explained above. Such cold rolling of the str p precludes the formation of stretcher strains which appear when annealed plain low carbon strip steel is stretched by tension from about one to five per cent or more, as explained above. If it is desired to roughen the surfaces of the strip, rol s I and D may be provided with roughened faces, or if it is desired to roughen only one surface of the strip the face of one or the other of these rolls may be roughened. If the face of drag roll D is roughened, the friction between it and the strip is increased with the result that the yield point line Y may move in a counter-clockwise direction on roll D, or in other words, further from the bite of rolls l and D than indicated in Fig. 1.

In a similar maner, a working roll 2 may be positioned below pull roll P to burnish the strip which is usually somewhat roughened when tensioned beyond its yield point, or the faces of rolls 2 and P may be roughened if it is desirable further to roughen the surfaces of the tensionstretched strip.

In the cold rolling of steel strip by rolls I and D and by rolls 2 and P I have found it advan tageous in the practice of this invention as applied to some products to limit the reductions taken to not more than about one-half of one per cent, as for example, when it is desired to have the surfaces of the strip smooth and free from blemishes. If reductions materially greater than this are taken scratch markings may appear on the surfaces of steel strip which make it unsuitable for some uses, as for example, when the strip is provided with thin coatings of metal.

In the cold processing of strip metal according to this invention the tensioning of the strip beyond its yield point is attended by a reduction in its width and thickness in proportion to the amount of tension applied to it. For example, an elongation of seven per cent is accompanied by a reduction in thickness of about five per cent and in width of about two per cent, the sum of the two being substantially equal to the elongation. In Fig. 2 there is showna face view of the portion of a strip being cold processed by the mill of Fig. 1, the strip being shown in flat form and its variations in width being exaggerated. On the strip there are shown in dot and dash lines the several successive stages in the processing of the strip, explained with reference to Fig. 1. The bite of rolls I and D upon the strip is shown by line R the yield point of the strip on drag roll D by line Y the line of tangency of the strip with the roll D by line T ,'the line of tangency of the strip with the roll P by line T the yield point of the strip on roll P by line Y v and the bite of rolls 2 and P upon the strip by line R Between lines R and Y there is a slight widening of the strip effected by rolling it. Between lines Y and T the strip in the gradually increasing plastic state becomes narrowed in width as generally indicated, the strip then being supported by roll D. Unrestrained elongation of the strip takes place between the tangency lines T and 'I' where the strip is unsupported and is shown as being materially contracted in width at a uniform rate. Between the tangency line 'I' and the yield point line Y on roll P the strip is further narrowed, as it is between lines Y and T, but at a progressively diminishing rate. Until the strip enters the bite of the rolls 2 and P it is in the elastic state and is not permanently narrowed, and beyond R it is shown as being slightly widened due to spreading action of those rolls. As shown in Fig. 2, the length of the portion of the strip between tangency lines T and 'I is materially less than its width so that the strip is maintained laterally stable and consequently free from longitudinal guttering.

By way of example, and not of limitation, I have found that low carbon strip steel twentyeight inches in width and 0.01 inch in thickness may be elongated solely by tension in the manner explained with reference to Fig. 1 on a mill whose rolls are positioned as there shown by using rolls twenty-four inches in diameter, rolls D and P being spaced twenty-seven and one-half inches center to center. By the use of drag and pull rolls of this size and spacing, the strip is elongated solely by tension applied to it beyond its yield point. The portion of the strip betweenyield point lines Y and Y is in the plastic state, and

each end of this portion of the strip is adjoined by a portion in the elastic state. If desired, or when operating conditions require it, additional drag and pull rolls may be used to increase the length of the strip wrapped upontheir faces so that there will be sufllcientfrictional engagement of the drag and pull rolls to maintain elastic state portions of the strip adjoining the plastic state portion. The use of such additional rolls will be explained in greater detail with reference to drawings of various mills that may be used.

In several respects strip steel that is tensiontempered according to this invention is superior to that tempered by cold rolling. For example, tin plate that is tempered by tension-stretching meets the non-fluting requirements of can bodies with a minimum of spring-back, and also meets the deep-drawing requirements of can tops. This is because strip that has been tension-tempered to a given hardness has materially greater ductility and attending drawability than a like strip that has been temper-rolled to the same hardness. An important difference between tensiontempered strip and temper-rolled strip arises from the fact that the tension-tempered product is cold worked substantially uniformly throughout its thickness, which is not the case with temper-rolled strip. The physical characteristics of the tension-tempered product strongly indicate that its grain structure has random as distinguished from preferred orientation. This has been confirmed by a micro-examination of the grain structure of tension-tempered as compared to temper-rolled steel strip. A further advantage of the properties of tension-tempered strip is that it can be used in making crimped-edge can bodies and the like without specific reference to the direction of the processing, which is not true with reference to temper-rolled steel.

As a specific example of the physical properties of strip steel that is tension-tempered according to this invention, a coil of annealed strip of rimmed steel stock .012 of an inch in thickness containing .09% carbon and .31% manganese had in its annealed state a Rockwell T hardness number of 50.7 and an Erickson value of 7'70. After being tension-tempered by stretching it four per cent it had a Rockwell T hardness number of 58.0 and an Erickson value of 570. This coil of strip steel was preworked by cold rolling it in which the reduction was one-half of one per cent. After such cold rolling it had a Rockwell T hardness number of 53.3 and an Erickson value of 720.

In the tin can industry there is an established range of tempers from Tl to T6, and higher for special cases. Tin plate of T,l temper has a Rockwell T hardness number of from about 46 to 52, while that having a T6 temper has a like hardness number of from about 66 to '70. The amount of stretch required in tension-tempering steel strip according to this invention varies according to the original hardness of the strip and also its chemical anaylsis, particularly its carbon content. I have found that when tension-tempering steel strip that is commonly known as high phosphorous tin plate analysis and which has a Rockwell T hardness of 48, a one per cent stretch gives a Tl temper, a two per cent stretch a T2 temper, a three per cent stretch a T3 temper, etc. When tension tempering strip of rimmed steel analysis somewhat more stretch is required, as for example, a T-4 temper requires an elongation of about six per cent.

Having reference now to mills on which strip steel may be tensioned beyond its yield point in the manner explained, the mill shown in Figs. 3 and 4 is equipped with two pairs of rolls which are positioned and arranged the same as shown in Fig. 1. These are drag roll D and working roll I which cooperates with it, and pull roll P and working roll 2 which cooperates with it. These rolls are suitably mounted in a housing consisting of side frames I and II, a base I2, and a top I3. The chocks which support the necks of rolls D and P' preferably position the axes of these rolls at a fixed distance from each other, while the chocks that support the necks of rolls I and 2 are movable vertically to vary the pass between each of them and the roll with which it cooperates. The chocks of upper roll I may be pressed upwardly against a screw-down by suitable roll balances. The screw-down mechanism, generally indicated at the top of the side frame II of the housing may be constructed like that shown in Patent No. 1,776,444 to McBane and Kline, to which reference may be made. Also, as generally indicated in Fig. 4 the checks of lower roll 2 may be urged upwardly by like screw-down mechanism to vary the pass between rolls 2 and P.

Drag roll D and pull roll P are caused to operate at different relative speeds by separate electrical power units, roll D being shown in Fig. 4 as being coupled to such a unit in the form of a motor [5 and pull roll P being driven by a motor I6.

These units or motors are operated through and controlled by suitable electrical equipment to the end that the difference in peripheral speeds between rolls D and P may be maintained constant within about one-tenth of one per cent regardless of variation in loads and of normal operating speeds. In the practice of this invention I have found that it is important to effect the desired control by maintaining constant the diflierence between these peripheral speeds, as distinguished from endeavoring to effect the control by maintaining constant tension in the portion of the strip being elongated. After a strip has been directed through the mill by suitable guides, which will presently be explained, the actual driving of the mill is effected entirely by motor I6 which drives roll P, motor I5 their acting as a regenerative brake upon drag roll D. Work roll I is preferably driven by friction through roll D, and similarly work roll 2 is driven by friction through roll P.

As shown in Fig. 3, strip S is preferably tensioned at the entry side of the mill by a pair of rolls 20 and Zn, and is similarly tensioned at the delivery side of the mill by a pair of rolls 22 and 23, around which pairs of rolls the strip is wrapped as shown. Each of rolls 20 and 2| is preferably coupled to a separate motor for driving it while the end of a strip is being guided through the mill, such motors becoming regenerative brakes to add tension to the strip as it passes through the mill during a cold processing operation. Similarly, each of rolls 22 and 23 is preferably driven by a separate motor, first to feed the entering end of the strip forwardly and then to apply tension to the strip as it is delivered from the mill. The strip may pass to tension rolls 20 and 2I from a suitable coil box or uncoiler 24, and beyond tensioning rolls 22 and 23 it may be coiled either tightly or loosely by a driven reel 29.

The tensioning of the strip at both the entering and delivery sides of the mill may be of the order of that similarly applied to strip metal when cold rolling it. Tensioning is necessary at the entering side of the mill if tension-stretching according to this invention is done without using roll I to exert pressure on the strip, as for example when there is no preworking of the strip between rolls I and D. Under similar operating conditions, tensionin is necessary at the delivery side of the mill.

Properly to direct the entering end of a strip around the several tensioning and processing rolls, suitable guides are provided. As shown in Fig. 3 an idle pressure roll 25 is positioned below tension roll 2|, such pressure roll preferably being formed of fiber or the like, and provision may be made in the usual or any desired way for lowering this roll from contact with the strip as soon as the end of the strip passe beyond it.

Beyond pressure roll 25, a stationary cylindrical guide 26-is positioned to cause the strip to bewrapped around roll 2|, and a similar stationary guide 21 is positioned adjacent to roll to cause the strip there is a removable pressure roll "similar in construction, function and operation to roll 25. Between tension roll 20 and the cooperating pair of rolls l and D there is a horizontal guide for supporting the entering end of the strip as it passes from roll 20 to the bite of rolls I and D. At the left end of guide 30 there is a roll 31 below the strip which, by a fluid pressure mechanism 33, may be moved from its dotted to its full line position after the leading end of a strip has been engaged by rolls 1 and D. By thus pressing the strip upwardly against the face of roll I, the strip becomes somewhat curved by the roll with the result that crimping of the edges of the strip and consequent impairment of it and marring of the faces of the rolls are prevented, at the tail end of the coil after tension is lost.

A stripper 3| ispositioned on the delivery side of roll I adjacent to its face to cause the entering end of the strip to turn downwardly and be engaged by a cylindrically shaped guide 32 adjacent to roll D which causes the strip to be wrapped around such roll. At the right of roll P there is'a guide 33 for causing the strip to be wrapped around roll P, such guide being preferably pivoted at its upper end and connected to the piston rod of a fluid pressure mechanism 36 to be wraDp d around it. Above roll 20 I which may be actuated to move the guide outwardiy to its dotted line position after a strip has been directed around roll P. Thus, if a strip should break between rolls D and P during a tension-stretching operation the broken end of the strip will not be guided into the bite of rolls 2 and P where it might cobble and mar the faces of the rolls, but will pass downwardly to the right of these rolls into a pit between the side frames of the housing. At the delivery side of rolls 2 and P there is a stripper 34 followed by a horizontal guide 35 for directing the strip to tension roll-s 22 and 23 which are equipped with pressure rolls and guides the same as tension rolls 20 and 2|.

It has been found that by using guides such as shown and described the entering end of a both the tensioning and processing rolls so that processing of the strip may be started as soon as the end of the strip has been wrapped around pull roll P.

Processing of the strip is efiected at high delivery speeds. In the practice of this invention strip has been passed through a mill like that shown in Figs. 3 and 4 at rates up to three thousand feet per minute, and higher speeds are considered entirely possible. It has been found that the rolls of the mill operate at much lower temperatures than the rolls of conventional temper mills whose delivery speeds are limited because coolants can not be used in temper rolling. The heating of rolls in temper mills is caused primarily by deformation of the strip, friction between the rolls and the strip, and friction in the roll neck bearings. In the mill provided according to this invention the heat imparted to the rolls by these causes is approximately one-third of that imparted to the rolls of conventional temper mills. This is due to the'fact that the roll pressures are materially lower, they being in the order of one-fifth of those in conventional temper rolling mills, and also to the fact that deformation of material by tension is effected at a much higher efliciency than deformation by dni= pression rolls.

\ In Fig. 5 there is diagrammatically illustrated a mill equipped with pairs of rolls the same as that shown in Figs. 3 and 4 in which the drag and pulls P and D are driven by a single motor 40 through intermeshing gears 4| and 41 which give a fixed and unvariable difference in the per pheral speeds of rolls D and P. By substitutinfi gears 4i and 42 of different ratios, different rein-'- tive peripheral speeds of rolls D and P may effected.

In Fig. 6 there is diagrammatically illustrated another mill equipped with rolls the same as shown in Figs. 3 and 4, but in which rolls D and P are driven by a single motor 45 through a differential which may be controlled by another motor to effect any desired difference in the peripheral speeds of rolls D and P. As shown, the drive shaft of motor 45, which is directly connected to pull roll P, is equipped with a beveled pinion 43 which meshes with a beveled pinion ill that is connected to the driving side of a differential 48. The driven side of this difierential is connected by a shaft 43, beveled pinions 50 and 5| to drive or control the peripheral speed of roll D. A motor 52 may be connected to the difierential variably to control the relative peripheral speeds of rolls D and P. In such a drive suitable controls for the two motors is required to obtain the desired results. Y

In Fig. 7 there is diagrammatically illustrated a mill in which two drag and "two pull rolls are substituted for the single drag and pull rolls of the mill of Figs. 3 and 4. The two drag rolls are indicated at D and D and the two pull rolls at P and P Positioned above roll D there is a working roll la, and positioned below pull roll P there is a working roll 20 corresponding, respec the strip is wrapped around pull rolls' P and P which are also spaced apart and driven at like peripheral speeds. beyond its yield point takesplace between drag roll D and pull roll P which are spaced apart as shown similar to the spacing of such rolls in the mill of Figs. 3 and 4. These additional drag and pull rolls may be used to give greater frictional engagement of strips to augment the tension in the strip when needed.

, The frictional engagement of the strip with the drag and pull rolls may also be increased by offsetting the rolls in the manner diagrammatically illustrated in Fig. 8, which shows a mill equipped with the same number of rolls as that of Fig. 7. In the mill of Fig. 8 drag rolls D and D are positioned in vertical alignment with work roll lb, and pull rolls P and P are positioned in vertical alignment with work roll 2b, but rolls P, P and 2b are offset laterally from the other rolls. Such an arrangement affords additional surface wrapping of the strip on the faces of drag roll D and pull roll P, the elongation being effected between these rolls as in the other forms of mills, and also makes it possible to shorten the drag rolls D and D are positioned in vertical The tensioning of the strip a? alignment with a work rbll lo. and two pull rolls P and P are positioned in vertical alignment with a work roll 2e, the elongation of the strip being effected between drag roll D and pull roll 1 as in the 'case or the mills shown in Figs. '1 and 8, both drag rolls are driven at the same peripheral speed, and both bull rolls are driven at the same peripheral speed greater than that of the drag rolls. Such an arrangement of rolls makes it possible toshortn the height of the roll housing and to place the screwdown of both hi the work rolls lo and 20 at the same end of the housing, as indicated. I H

In the mill shown in Figs drag roll D and work roll Id are positioned in vertical alignment at one side, and pull roll P and work roll id in vertical alignment at the other side of a housing. The pull and drag rolls being spaced laterally from each other a greater distance than in the mill shown in Fig. 9, an idle roll 55 is positioned below the strip between pull roll P and drag roll D to shorten the unsupported length of the plastic state portion of the strip between these rolls so that the strip may be maintained laterally stable and consequently free from longitudinal gutterins.

Among the important advantages of the invention are the improvement in product resulting from the practice of the method, as has been explained, and a greatly reduced cost of cold processing strip metal by tensioning as compared to cold rolling. As to cost, by one pass of strip steel through a single stand tension-tempering mill like that shown in Figs. 3 and 4 the strip may be given the highest temper now specified. This requires two or three passes through a temper rolling mill which involves much higher labor cost than a single pass through th tensioning-tempering mill. Also, the initial cost of a tension-tempering mill and its accessory equipment is about forty per cent of that of the usual two-stand temper-rolling mill andits accessory equipment, and is about two-thirds the cost of a single stand temperrolling mill and its accessory equipment. Because low roll pressures are advantageously used in the operation of the tension-tempering mill, smaller and less expensive roll bearings and mill housings may be used, and also cheaper roll making materials, and the roll maintenance costs are greatly reduced as compared to temper-rolling mills which operate under high roll pressures. Operating costs are further reduced because of the high speed of operation arising from the fact that the tension-tempering mill runs much cooler than temper-rolling mills.

According to the provisions of the Patent Statutes, I have explained the principle of my invention and have illustrated and described the preferred mode of and mills for practicing it. However, I desire to have it understood that, within the scope of the appended claims, my invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. The continuous method of cold processing a wide thin strip of metal by progressively tensioning it beyond its yield point, comprising wrapping the strip partially around parallel drag and pull rolls frictionally to engage a relatively large portion of the face of each. a portion of the strip between said rolls being free from engagement with them, driving the drag roll at a pre-determined peripheral speed, rolling the strip on said drag roll to cold work it and thereby preclude it from stretcher strains in its subsequent tensioning, and driving the pull roll at a peripheral speet! greater than that of the drag roll progressively to stretch solely by tension beyond its yield point the portion of the strip that moves continuously from the drag to the pull roll, such portion or the strip then being in the plastic state induced by thus tensioning it and the ends thereof being im mediately adioined by strip portions in the elastic state wrapped on said drag and pull rolls, the unsupported length of the strip between said rolls being short enough with relationto its width to maintain the strip laterally stable and consequently free from longitudinally guttering.

2. The continuous method of cold processing a wide thin strip of metal by progressively tensioning it beyond its yield point, comprising wrapping the strip partially around parallel drag and pull rolls frictionally to engage a relatively large portion of the face of each, a portion of the strip between said rolls being free from engagement with them, driving the drag roll at a pre-determined peripheral speed, driving the pull roll at a peripheral speed greater than that of the drag roll progressively to stretch solely by tension beyond its yield point the portion of the strip that moves continuously from the drag to the pull roll, such portion of the strip then being in the plastic state induced by thus tensioning it and the ends thereof being immediately adJoined by strip portions in the elastic state wrapped on said drag and pull rolls, the unsupported length of the strip between said rolls being short enough with relation to its width to maintain the strip laterally stable and consequently free from longitudinal guttering, and rolling the strip on said pull roll.

3. The continuous method of tempering a wide thin strip of steel by progressively tensioning it beyond its yield point while the strip is at a cold working temperature, comprising wrapping the strip partially around parallel drag and pull rolls frictionally to engage a relatively large portion of the face of each, a portion of the strip between said rolls being free from engagement with them,

driving the drag roll at a pre-determined peripheral speed, rolling the strip on said drag roll to cold work it and thereby preclude it from stretcher strains in its subsequent'tensioning, and driving the pull roll at a peripheral speed greater than that of the drag roll progressively and permanently to stretch solely by tension the portion of the strip that moves continuously from the drag to the pull roll, such portion of the strip then being in the plastic state induced by thus tensioning it and the ends thereof being immediately adjoined by strip portions in the elastic state wrapped on said drag and pull rolls, the unsupported length of the strip between its lines of tangency with said rolls being not greater than its width to maintain the strip laterally stable and consequently free from longitudinal guttering.

4. A continuous mill for progressively tensioning beyond its yield point and while cold-a wide thin strip of metal, comprising a roll housing, a pair of cooperating work-reducing rolls mounted in said housing one of which is a drag roll, a

second pair of work-reducing rolls mounted in said housing in spaced relationship with said firstmentioned pair, one of said second pair being a pull roll; means for directing the strip in sequence between said first-named pair of rolls thereby to cold roll it, around a relatively large portion of the face of the drag roll thereof frictionally to engage it, around a relatively large portion of the face of said pull roll of said secand pair of rolls frictionally to engage it, and

between said second pair of rolls thereby to roll 4 mounted in said housing in closely spaced relationship with said first-mentioned pair and in vertical alignment therewith, one of said second pair being a pull roll; means for directing the strip in sequence between said first-named pair of rolls, around a relatively large portion of the face of the drag roll thereof, around a relatively large portion of the face of said pull roll of said second pair of rolls, and between said second pair of rolls; and means for driving said pull roll at-a peripheral speed materially greater than that of said drag roll progressively to stretch solely by tension beyond its yield point the portion of the strip that moves continuously from said drag to said pull roll.

6. A continuous mill for progressively tensioning beyond its yield point and while cold a wide thin strip of metal, comprising a roll housing, a pair of cooperating work-reducing rolls mounted in said housing one of which is a drag roll, a, screw-down at the top of the housing for controlling and adjusting the pass between said pair of rolls, a second pair of workreducing rolls mounted in said housing in spaced relationship with said first-mentioned pair one of said second pair being a pull roll, a screw-down at the bottom of the housing for controlling and adjusting the pass between said second pair of rolls; means for directing the strip in sequence between said first-named pair of rolls, around a relatively large portion of the face of the drag roll thereof, around a relatively large portion of the face of said pull roll of stretch solely by tension beyond its yield point.

the portion of the strip that moves continuously from said drag to said pull roll.

7. A mill for progressively tensioning beyond its yield point and while cold a wide thin strip of metal, comprising a roll housing, a pair of vertically-aligned cooperating working rolls mounted in said housing one of which is a drag roll, a screw-down for controlling and adjusting the pass between said pair of rolls, a second pair of vertically-aligned working rolls mounted in said housing in spaced relationship with said first-mentioned pair and in vertical alignment therewith, one of said second pair being a pull roll; guide means for directing the strip in sequence between said first-named pair of rolls thereby to cold roll it, around a relatively large portion of the face of the drag roll thereof frictionally to engage it, around a relatively large portion of the face of said pull roll of said second pair of rolls frictionally to engage it, and

between said secondpair of rolls thereby to roll of said drag roll progressively to stretch solely by tension beyond its yield point the portion of the strip that moves continuously from said drag to said pull roll.

8. A continuous mill for progressively tensioning beyond its yield point and while cold a wide thin strip of metal, comprising a pair of cooperating work-reducing rolls one of which is a drag roll, a second pair of work-reducing rolls mounted in spaced relationship with said firstmentioned pair, one of said second pair being a pull roll: guides for directing the leading end of a strip in sequence between said first-named pair of rolls, around a relatively large portion of the face of the drag roll thereof, around a relativel large portion of the face of said pull roll of said second pair of rolls, and between said second pair of rolls; the guide for directing the strip around said pull roll being movable laterally of the pull roll to a non-guiding position during the tension stretching of the strip; and means for driving said pull roll at a peripheral speed materially greater than that of said drag roll progressively to stretch solely by tension beyond its yield point the portion of the strip that moves continuously from said drag to said pull roll.

9. A mill for progressively tensioning beyond its yield point and while cold a wide thin strip of metal, comprising a roll housingfa pair of vertically-aligned cooperating working rolls mounted i said housing one of which is a drag roll, a second pair of vertically-aligned cooperating working rolls mounted in said housing in spaced relationship with said first-mentioned pair, one of said second pair being a pull roll; guides for directing the strip in sequence between said first-mentioned pair of rolls, around a relatively large portion of the face of the drag roll thereof, around a relatively large portion of the face of said pull roll of said second pair of rolls, and between said second pair .of rolls; means for driving said pull roll at a peripheral speed materially greater than that of said drag roll progressively to stretch solely by tension beyond its yield point the portion of the strip that moves continuously from said drag to said pull roll; and means for tensioning the strip below its yield point as it enters said first-men'- tioned pair of rolls and as it is delivered from said second pair of rolls.

10. The continuous method of cold processing a wide thin strip of metal by progressively tensioning it beyond its yield point, comprising wrapping the strip partially around parallel drag and pull rolls frictionally to engage a relatively' large portion of the face of each, a portion of the strip between said rolls being free from engagement with them, driving the drag roll at a predetermined peripheral speed, rolling the strip on the drag roll to cold reduce it not more, than about one-half of one per cent and thereby preventing it from being scratched by slipp e on the surface of thedrag roll and preclude it from stretcher strains in the subsequent tensioning, and driving the pull roll at a peripheral speed greater than that of the drag roll progressively to stretch solely by tension beyond its yield point the portion of the strip that moves continuously from the drag to the pull roll, such portion of the strip then being in the plastic state induced by this tensioning it and the ends thereof being immediately adjoined by strip portions in the elastic state wrapped on said drag and pull rolls, the unsupported length of the strip be- 15 tween said rolls being short enough with relation to its width to maintain the strip laterally stable and consequently tree from longitudinally guttering.

11. A continuous mill for progressively tensioning beyond its yield point and while at a cold-working temperature a wide thin strip of metal, comprising a pair of cooperating workreducing rolls one of which is a drag roll, a second pair of work-reducing rolls in closely spaced relationship with said first-mentioned pair, one oi said second pair being a pull roll; means for directing the strip in sequence between said first-named pair of rolls, around a relatively large portion of the face of the drag roll thereof, around a relatively large portion of the face of said pull roll of said second pair of rolls, and between said second pair of rolls; and means for driving said pull roll at a pre-determined speed materially greater than that of said drag roll progressively to stretch solely by tension beyond itsyield point the portion of the strip that moves continuously from said drag to said pull roll.

MORRIS D. STONE.

16 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 312,608 Britton Feb. 24, 1885 556,193 Matthews Mar. 10, 1896 1,983,387 Mohler Dec. 4, 1934 2,040,442 Nleman May 12,1936 2,176,094 Moore Oct. 17, 1939 2,177,711 Graham Oct. 31, 1939 2,226,948 Simons 1 Dec. 31, 1940 2,287,380 Klein June 23, 1942 2,291,361 Walsh July 28, 1942 2,306,792 Moore Dec. 29, 1942 2,316,067 r Hickman Apr. 6, 1943 2,332,796 Hume Oct. 26, 1943 2,332,803 Lorig Oct. 26, 1943 FOREIGN PATENTS Number Country Date 252,151 Germany Oct. 16, 1912 

